The present invention relates generally to an anchor device and more particularly to such a device which is designed to be secured within a bore formed in a masonry or concrete structure which structure is formed by utilizng relatively hard aggregate.
The securement techniques of devices, attachments, fixtures, etc. to concrete or masonry structures has typically utilized stud-like devices which are inserted in a bore or hole preformed in the masonry. The stud-type anchor must in some way be activated to create a wedging or slight imbedment within the walls of the concrete to properly provide suitable pull out strength in such applications. Recent advances in the art of securement to masonry structures have included screw threaded type anchors which threadingly engage the walls of a bore in the masonry or concrete. Examples of these screw anchors are shown in patents such as U.S. Pat. Nos. 3,902,399 and 3,937,119.
While devices of the type generally described in these prior art patents may be suitable for some compositions of masonry or concrete, it has been found that certain geographical areas form concrete or masonry with aggregate of relatively hard materials, such as granite or the like. Such material creates problems in screw type anchors of the prior art being unable to penetrate the walls of the bore or very large torque requirements being necessary to imbed the threads into the walls. It should be understood that the term masonry used herein is intended to be generic to stone-like building materials and includes but is not necessarily limited to, concrete, brick, fire brick materials, ceramic materials, etc.
It has been found that, even within the crowded art of threaded fasteners, a unique relationship between the several parameters of a threaded fastening system in concrete or masonry exists which will permit such a system to work effectively and efficiently in hard aggregate concrete. The instant invention therefore describes a unique relationship which includes a sharp crested thread having an included angle in the range of 50.degree. to 65.degree., and a lead angle of the helix on the shank in the range of approximately 6.degree. to 81/2.degree. and a predetermined relationship between the diameter bore formed in the concrete or masonry and the crest diameter of the threaded fastener to provide imbedment in the walls of the bore of approximately 0.05 the crest diameter of the fastener. Such a fastener system has been found to penetrate hard aggregate masonry or concrete material using acceptable application torque and provide acceptable pull out strengths.